Double layer capacitors are electrical storage devices which fulfill the need for reserve power sources for microcomputers. The devices are small in size but have enough capacitance to serve as a power source for a sufficient time to protect the computer memory from erasure during a power failure or shut down.
Double-layer capacitors are described in the Hosokawa et al. U.S. Pat. No. 4,313,084, Jan. 26, 1982. In such capacitors, carbon pastes made of fine activated carbon powder having a high surface area are mixed with a sulfuric acid electrolyte and formed into electrodes of a capacitor. The electrodes are separated by a porous separator which functions as an electronic insulator and allows ionic conduction. Such carbon paste capacitors are reported to have high capacitance attributed to the high surface area of the carbon particles. Similar carbon paste capacitors are described in the Boos U.S. Pat. No. 3,536,963, Oct. 27, 1970. In both of the patents referred to above, the capacitors consist of a pair of identical electrode assemblies made up of carbon paste and an electrolyte. Similar capacitors are described in an article by Sanada and Hosokawa in NEC Research & Development, No. 55, October 1979, pp. 21-27. Because of the large surface area of the activated carbon particles, the capacitors have a large capacitance for a relatively small size.
The Boos et al. U.S. Pat. No. 3,648,126, Mar. 7, 1972, describes electrical capacitors with paste electrodes of the type referred to above. In these capacitors, one electrode is a paste of carbon particles of high surface area mixed with an alkaline electrolyte and the other electrode is composed of powdered metal and electrolyte. The powdered metal is described as copper, nickel, cadmium, zinc, iron, manganese, lead, magnesium, titanium, silver, cobalt, indium, selenium and tellurium, of particle size less than 10 microns.